This invention relates to a field emission type display device having field emission cathodes incorporated therein, and more particularly to an improvement in a display device wherein the whole device including peripheral equipments is integrally constructed while having field emission cathodes known as a cold cathode incorporated therein.
It has been wide known that when an electric field applied to a surface of a metal material or that of a semiconductor material is set is to be about 10.sup.9 (V/m), a tunnel effect occurs to permit electrons to pass through a barrier, resulting in the electrons being discharged to a vacuum even at a normal temperature. Such a phenomenon is referred to as "field emission" and a cathode constructed so as to emit electrons based on such a principle is referred to as "field emission cathode" (hereinafter also referred to as "FEC").
Recent rapid development of semiconductor processing techniques permits a field emission cathode, in particular, of the surface discharge type to be formed of field emission cathode elements of a size as small as microns. A device which is so constructed that a plurality of such FEC elements of the surface discharge type are arranged on a substrate and electrons emitted from emitters of the FEC elements are impinged on phosphors, to thereby cause the phosphors to selectively emit light is expected to be widely used as a main component for various kinds of display devices and electronic devices generally formed into a flat shape.
The FEC element described above may be manufactured by a rotary oblique deposition process developed by Spindt, which is disclosed in U.S. Pat. No. 3,789,471. Also, the FEC element may be manufactured by subjecting a silicon single-crystal plate to selective etching. The former method exhibits an advantage of permitting a cathode tip material to be freely selected as desired and the latter method has an advantage of permitting current semiconductor fine processing techniques to be applied thereto without modifying the techniques.
Now, a conventional FEC manufactured according to the Spindt process will be described with reference to FIGS. 33(a) and 33(b).
An FEC shown in FIG. 33(a) is formed by first depositedly forming a conductive layer 100 of a thin film for a cathode electrode on an insulating substrate 100 made of glass or the like and then forming a film of silicon (Si) doped with impurities on the conductive layer 101 to form a resistive layer 102. Then, a gate electrode layer 104 is depositedly formed of niobium (Nb) on the resistive layer 102 through an insulating layer 103 made of silicon dioxide (SiO.sub.2) and then holes 114 are formed through the insulating layer 103 and gate electrode layer 104 to expose a part of the resistive layer 102. Thereafter, molybdenum (Mo) or the like for emitters is positively deposited on an exposed surface of the resistive layer 102, to thereby form emitters 115 of a conical shape.
Thus, the Spindt process permits a distance between the conical emitters 115 and the gate electrode layer 104 to be less than a micron, so that emission of electrons from the emitters 115 may be accomplished by merely applying a voltage as low as tens of volts between the emitters 115 and the gate electrode layer 104.
An FEC shown in FIG. 33(b) is formed into a so-called triode structure. More particularly, a second gate electrode layer 108 is laminatedly formed on a gate electrode layer 104 through an insulating layer 107. The second gate electrode layer 108 functions to focus electrons emitted from emitters 115. The remaining part of the FEC may be constructed in substantially the same manner as that shown in FIG. 33(a).
The FEC elements constructed as shown in FIGS. 33(a) and 33(b) each may be used for constructing a display device. For example, FIG. 34 shows a display device having the FEC element shown in FIG. 33(b) incorporated therein by way of example. More particularly, the display device of FIG. 34 is so constructed that an anode substrate 116 having phosphors deposited thereon is arranged above the insulating substrate 100 having a plurality of the FEC elements formed thereon in an array-like manner, wherein a control voltage V.sub.G1 is applied to the first gate electrode 104, a voltage V.sub.G2 for focusing electrons emitted is applied to the second gate electrode 108, and an anode voltage V.sub.A is applied to the anode substrate 116, resulting in the phosphors deposited on the anode substrate 116 being selectively excited for luminescence by electrons emitted from emitters 115.
Now, a drive mechanism for the display device constructed as described above using the FEC elements will be described hereinafter with reference to FIG. 35.
The drive mechanism, as shown in FIG. 35, includes a display controller 120, a cathode-side driver 121, a gate-side driver 122 and a display region 123 constructed in such a manner as shown in FIG. 34 and having image cells of nxm in number. The display controller 120 feeds the cathode-side driver 121 with a vertical scan timing, so that the driver 121 applies a scan voltage to cathodes C.sub.1 to C.sub.n in order. Also, the gate-side driver 122 applies a data voltage to gates G.sub.1 to G.sub.m depending on display data.
In the drive mechanism thus constructed, image cells (FECs) in a cathode line being scanned each emit electrons toward an anode electrode depending on a gate voltage applied in correspondence to the display data, to thereby permit display desired to be carried out. However, the display region 113 fails to operate under the conditions that a voltage of a TTL level (about 5 V) is applied. In other words, application of a voltage of a level as output from the display controller 120 fails to permit the display region 123 to exhibit display.
In view of the above, the cathode-side driver 121 and gate-side driver 122 each are provided with a voltage level conversion section for converting a voltage of a TTL level into an FEC operation voltage. This requires to arrange the voltage level conversion sections of nxm in number in correspondence to the cathodes C.sub.1 to C.sub.n and gates G.sub.1 to G.sub.m. Also, the cathode-side driver 121 and gate-side driver 122 each are required to be constructed as a unit independent from the display region 123.
Thus, in the display device having the FEC elements incorporated therein which is constructed as described above, the cathode-side driver 121 and gate-side driver 122 must be constructed into units independent from each other, respectively, to thereby cause large-sizing of the display device and an increase in manufacturing cost. Also, the conventional display device requires voltage level conversion sections of nxm in number, so that a circuit of the display device is highly complicated.
Such a display device is normally provided with a data holding circuit or memory circuit for every image cell, so that data stored in the circuit are applied in the form of a control voltage to the gate electrodes. Such construction permits static display to be carried out at a substantially reduced drive voltage while exhibiting increased luminance, as compared with dynamic display. Thus, the display device is effective and suitable for static display. In particular, in view of the fact that in such a display using FEC elements, an increase in luminance requires an increased voltage, so that static display is highly desirable.
Conventionally, in order to provide each of image cells of the display device with a memory function, a thin film transistor type liquid crystal display (TFT-LCD) device and a plasma display (PDP) device have been conventionally known in the art. In the above-described display device having the FECs incorporated therein, it would be considered that a combination of the TFT systems provides each of the image cells with the memory function. Unfortunately, this renders a manufacturing process of the display device extensively complicated to a degree sufficient to render the manufacturing substantially impossible.
Also, when it is desired to provide the display with gradation in the display device using the FECs, it would be considered that image data are fed to the device while being subject to pulse width modulation (PWM) and gradated display required is carried out by controlling a period during which luminescence is carried out. However, this likewise results in construction of the display device being highly complicated.